Cancer cells often develop resistance to various chemotherapy agents. One of the mechanisms that contributes to such resistance is the elevation of Clusterin in its secreted form.
Clusterin (also known as CLU, Apolipoprotein J, ApoJ, testosterone repressed prostate message-2, TRPM-2, and sulfated glycoprotein-2) is a well known multifunctional, ubiquitously expressed protein that has been implicated in various cell functions including carcinogenesis and tumor progression.
Two Clusterin protein isoforms are known to be generated in human cells: a pro-apoptotic non-glycosylated nuclear form (nCLU) and a pro-survival glycosylated secreted form (sCLU) (Moretti R M, Marelli M M, Mai S, Cariboni A, Scaltriti M, Bettuzzi S, Limonta P. Clusterin isoforms differentially affect growth and motility of prostate cells: possible implications in prostate tumorigenesis. Cancer Res 2007; 67(21):10325-10333; Shannan B, Seifert M, Leskov K, Willis J, Boothman D, Tilgen W, Reichrath J. Challenge and promise: roles for clusterin in pathogenesis, progression and therapy of cancer. Cell Death Differ 2006; 13(1):12-1).
Upregulation of sCLU appears to be a general response to molecular stress. In particular, progression towards high-grade and metastatic carcinoma is correlated with a shift from nCLU to sCLU expression (Kurahashi T, Muramaki M Yamanaka K, Hara I, Miyake H. Expression of the secreted form of clusterin protein in renal cell carcinoma as a predictor of disease extension. BJU Int 2005; 96(6):895-899.)
In addition, sCLU is associated with resistance to various anti-cancer treatments including chemotherapy (Park D C, Yeo S G, Shin E Y, Mok S C, Kim D H. Clusterin confers paclitaxel resistance in cervical cancer. Gynecol Oncol 2006; 103(3):996-1000), radiotherapy (Cao C, Shinohara E T, Li H, Niermann K J, Kim K W, Sekhar K R, Gleave M Freeman M, Lu B. Clusterin as a therapeutic target for radiation sensitization in a lung cancer model. Int J Radiat Oncol Biol Phys 2005; 63(4):1228-1236), hormone ablation (Miyake H, Yamanaka K, Muramaki M Kurahashi T, Gleave M, Hara I. Enhanced expression of the secreted form of clusterin following neoadjuvant hormonal therapy as a prognostic predictor in patients undergoing radical prostatectomy for prostate cancer. Oncol Rep 2005; 14(5):1371-1375), and specific antibodies (Biroccio A, D'Angelo C, Jansen B, Gleave M E, Zupi G. Antisense clusterin oligodeoxynucleotides increase the response of HER-2 gene amplified breast cancer cells to Trastuzumab. J Cell Physiol 2005; 204(2):463-469).
Antagonists of sCLU have the potential to re-sensitize chemotherapy resistant malignancies.
Schmitz G. Drug evaluation: OGX-011, a clusterin-inhibiting antisense oligonucleotide. Curr Opin Mol Ther 2006; 8(6):547-554 describe OGX-011, a clusterin-inhibiting antisense oligonucleotide (ASO) as a potential treatment for increasing the susceptibility of resistant solid tumors (breast, non-small-cell lung and prostate) to conventional cancer therapies.
There have further been preliminary results demonstrating potential use of siRNA-mediated clusterin down regulation for treatment of cancers, such as colorectal cancer (Andersen C L, et al., Mol Cell Proteomics 2007; 6(6):1039-1048; Rodriguez-Pineiro A M, et al., Mol Cell Proteomics 2006; 5(9):1647-1657), melanoma (Shannan B, et al., Anticancer Res 2006; 26(4A):2707-2716), renal cell cancer (Zellweger T, et al., Neoplasia 2001; 3(4):360-367), bladder cancer (Chung J, et al., Cancer Lett 2004; 203(2):155-161; Miyake H, et al., J Urol 2004; 171(6 Pt 1):2477-2481; Miyake H, et al., Clin Cancer Res 2001; 7(12):4245-4252; Miyake H, et al., Neoplasia 2005; 7(2):171-179; Yamanaka K, et al., Oncol Rep 2005; 13(5):885-890) and pancreatic cancer (Xie M J, et al., Pancreas 2002; 25(3):234-238).
Clusterin is further involved in the epithelial-to-mesenchymal transition of carcinoma cells. WO2007/030930 describes agents (such as monoclonal antibodies), having binding-activity to clusterin, which inhibit the epithelial-to-mesenchymal transition (EMT) in carcinomas.
Furthermore, the level of clusterin is increased in the hippocampus and frontal cortex of the brains of Alzheimer's Disease patients. It is currently believed that clusterin, by binding to beta-amyloid, a protein known to aggregate in the brains of these patients, acts to link the progression of this disease to the complement system (Choi-Miura and oda, Neurobiol. Aging, 1996, 17, 717722).
sCLU in fact appears to be a part of the beta-amyloid complex and other complexes related to neurodegenerative disorders, and has been correlated to age-related macular degeneration (AMD) (An E, Lu X, et al., J Proteome Res 2006; 5(10:2599-2610), Alzheimer's Disease (AD) (Choi-Miura N H, et al., Neurobiol Aging 1996; 17(5):717-722), and Creutzfeldt-Jakob Disease (Freixes M, et al. Acta Neuropathol 2004; 108(4):295-301).
Clusterin is overexpressed in many disease states including neurodegenerative disorders, gliomas, and retinitis pigmentosa. Expression is induced in acute and chronic models of renal injury and disease, following ureter obstruction, ischemia/reperfusion, and atherosclerosis (Silkensen et al., Biochem. Cell. Biol., 1994, 72, 483-488).
Clusterin is also expressed in M cells (microfold cells) and follicular dendritic cells at inductive sites of human mucosa-associated lymphoid tissue (Waelput W et al., Histochem Cell Biol. 2007 Dec. 21).
Clusterin has further been implicated in various physiological processes and physiological disturbance states including ageing, cancer progression, vascular damage, diabetes, kidney and neuron degeneration (Ioannis P. Trougakos & Efstathios S. Gonos; Free Radical Research, December 2006; 40(12): 1324-1334). Although unrelated in their etiology and clinical manifestation, these diseases represent states of increased oxidative stress, which in turn, promote amorphous aggregation of target proteins, increased genomic instability and high rates of cellular death. Among the various properties attributed to clusterin so far, those mostly investigated and invariably appreciated are its small heat shock proteins-like chaperone activity and its involvement in cell death regulation, which are both directly correlated to the main features of oxidant injury. Moreover, the presence of both a heat shock transcription factor-1 and an activator protein-1 element in the clusterin gene promoter indicates that the clusterin gene can be an extremely sensitive biosensor to reactive oxygen species.
To date, there are no known therapeutic agents which effectively inhibit the synthesis of clusterin. Investigative strategies aimed at modulating clusterin function have involved the use of antibodies, antisense oligonucleotides and chemical inhibitors. As in all technologies at all times, these agents can be improved upon and there remains a need for additional agents capable of effectively inhibiting clusterin.